1. Field of the Invention
This invention relates to subsea wellhead systems, and more particularly to a guidelineless system for entry or reentry into a subsea wellhead.
2. Description of the Prior Art
The production of oil and gas from offshore wells has developed into a major endeavor of the petroleum industry. Wells are commonly drilled several hundred or even several thousand feet below the surface of the ocean. These wells must not only be drilled without the use of divers at the deeper depths, but the connecting, testing and servicing of pipes and of regulating valves must be performed on these wells during and after the drilling process.
Some of the prior art wellhead facilities include a foundation causing which is connected to a wellhead guidebase and having a plurality of guideposts connected to the guidebase. A separate guide cable is connected between each of the guideposts and a surface vessel so that the subsea tree, blowout preventers, valves and service tools can be guided into position on the well by these guide cables. If these guide cables break or become entangled it is expensive to correct the problem and to lower the equipment to the wellhead. If the well should be temporarily abandoned it is necessary to remove the cables from the guideposts so that the cables can be retrieved. If it is desired to reenter the well at a later time it is necessary to send divers to the seafloor to connect new cables to the guideposts. In deeper water this is impossible to do; and even in shallower water this procedure is expensive.
Some of the prior art wellhead facilities include guidelinesless apparatus having TV/sonar guidance equipment which uses TV and sonar for visual guidance of working tools into position to remove the tree assembly from the seafloor and raise the tree assembly to a surface vessel for repair and service. This prior art equipment does not have the accuracy and dexterity of movement required for much of the repair work on the equipment at the seafloor. Therefore, the tree assembly must be removed and brought to the surface for some of the repair work, a procedure which is time consuming and expensive.
What is needed is apparatus which can be used to guide the service and repair equipment into precisely defined positions adjacent the wellhead so that service work and repairs can be done on the tree assembly, valves, etc. without the time and expense of bringing these elements to the surface vessel.